HOW TO PREVENT CANCERS

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6 Ways to Prevent Breast Cancer

Thursday, October 6, 2011 0 comments

Ask women what they think is the biggest threat to their health, and most will answer “breast cancer.” And even though lung cancer and heart disease kill more women each year, their concern is well placed.

Breast cancer is the most common cancer among women in the US -- about 230,000 American women are diagnosed with the disease each year -- and it is the leading killer of women in midlife (ages 30 – 55). And despite thousands of studies on the causes of breast cancer, not many lifestyle factors have been linked to the disease, leaving many women frustrated that there’s not more they than can do to try to lower their risk.

Yet, looked at as a whole, there are a number of important steps women can take to try to prevent breast cancer. Not every one applies to every woman, but together than can have a big impact on risk:

Six Ways to Prevent Breast Cancer

1) Keep weight in check

No surprise here. Women who maintain a healthy weight have a lower risk of breast cancer, especially when they’re post-menopausal. One reason for this is that fat tissue produces hormones that increase the risk of breast cancer. The less fat tissue, the lower the hormone levels, and the lower the risk of breast cancer.

2) Be physically active

Exercise is as close to a silver bullet for health as there is. People who are physically active for at least 30 minutes a day have a lower risk of breast cancer, possibly because exercise has a positive effect on the levels of hormone and other growth factors in the body. Being physically active is also one of the best ways to help keep weight in check.

3) Avoid too much alcohol

Yes, alcohol can be good for your heart, but when it comes to cancer there’s not too much good about it. Even moderate amounts increase the risk of colon cancer and breast cancer. And studies show that women who have less than one drink a day have a lower risk of breast cancer than those who drink more.

If you do drink moderately, there’s evidence that the vitamin folate - in the amount found in most 100 % DV multivitamins and B-complex vitamins – may help protect against the increased risk associated with alcohol.

In general, if you drink moderately (no more than 1 drink a day for women) the overall health benefit of drinking outweigh the risks. But if you don’t drink, don’t feel that you need to start. If you have any concerns, talk to a doctor about how alcohol may affect your health.

4) Breastfeed, if possible

OK, this only applies to women who are still having children, but there is very good evidence that breastfeeding has real benefits for mother and child. When it comes to breast cancer, women who breastfeed for a total of one year or more (combined for all children) have a lower risk of the disease. Why? Breastfeeding can cause changes both in hormone levels and in the breast tissue itself that help protect the cells from becoming cancerous. Women who regularly breast feed also have a lower risk of ovarian cancer.

5) Avoid birth control pills, particularly after age 35 or if you smoke

As many women know, birth control pills have real, practical benefits. But, they can have some downsides, too. Women currently on birth control pills have an increased risk of breast cancer as well as a higher risk of stroke and heart attack – particularly if they smoke. Since their long term use, though, can lower the risk of colon cancer, uterine cancer and ovarian cancer – not to mention unwanted pregnancy - there’s also a lot in their favor. If you’re particularly concerned about breast cancer risk, avoiding birth control pills can lower your risk. Even if you take birth control pills, though, risk only seems to be increased during the time you’re actively on them.

6) Avoid post-menopausal hormones

Even if you’ve wanted to, it’s been hard to avoid the topic of post-menopausal hormones the past number of years, the way it’s swept the health news, confusing thousands along the way. In a nutshell, here’s what you need to know about how they can affect the risk of breast cancer and other important diseases.

When all the evidence is looked at together it’s clear that post-menopausal hormones shouldn’t be taken long term to prevent chronic diseases, like osteoporosis and heart disease. Estrogen-only hormones don’t lower the risk of heart disease, and actually increase the risk of breast cancer and stroke. And estrogen plus progestin hormones—the type of hormones taken most often by women with a uterus—raise the risk of breast cancer, heart disease, stroke, and blood clots. While both types of hormones lower the risk of osteoporosis, this benefit is usually offset by their risks, especially since there are many other options for combating bone loss and fractures.

Whether women should take post-menopausal hormones in the short term to treat menopausal symptoms like hot flashes is a personal decision. Hormones can bring significant relief from unpleasant, irritating, and sometimes severe symptoms, and the risks are relatively small from 1- 2 years of hormone use, especially for estrogen-alone in women without a uterus. If women do take hormones, it should be for the shortest time possible. As always, the best person to talk to about the risks and benefits of post-menopausal hormones is a doctor.

Tamoxifen and Raloxifene

Allthough not really a “healthy behavior” as most would describe it, if you’re at high risk of breast cancer, taking the prescription drugs tamoxifen and raloxifene can significantly lower your risk. They are powerful drugs, though, and can also have serious side effects, so are not right for everyone and can only be prescribed by a doctor. If you think you’re at high risk, talk to your doctor to see if these drugs may be right for you.

What about Soy?

No doubt you’ve heard a lot about soy in recent years as a way to boost your health, and there is growing evidence that a high-soy diet is both safe to eat and could help lower the risk of breast cancer. The amount of soy that seems to bring benefits, though, is much higher than even big soy eaters in the US typically consume. So, it’s unclear how realistic it is for most women to eat enough to begin to see breast health benefits.

Importance of Screening

Despite recent news storms on breast cancer screening, it remains the single best way to protect yourself from the disease. Though it doesn’t help prevent cancer, it can help find cancer early when it’s most treatable.

All women over the age of 20 should get screened regularly for breast cancer. The right screening tests mainly depend on a woman's age:

If you are between ages 20 and 39: Get a clinical breast exam every 1 - 3 years.

If you age 40 or older: Get a mammogram and clinical breast exam every year.

If you’re at high risk, you may need to have mammograms more often and begin them at an earlier age. You may also need to have some different types of screening tests.

And don't rely on finding breast cancer yourself with self-exams. Though it’s OK to do breast self-exams, they don't take the place of mammograms and clinical breast exams.

Estimating Your Breast Cancer Risk

Online tools for estimating breast cancer risk abound, and many of these sites can be useful guides for opening a dialog with doctors or other health professionals about your cancer risk and health choices.

Not all risk assessment sites, though, are created equal, and it’s good to do some research before using them. As with most health information on the Internet, it’s best to start with sites from known reputable organizations, such as universities, large health organizations, and the federal government. When seeking out cancer risk assessment tools, it’s also very important to look for information showing that developers of the site have experience in the field. While it’s easy to put up a cancer risk quiz on the web, it’s much harder to get it right. 

Two of the best-established cancer risk estimation sites are the National Cancer Institute’s “Breast Cancer Risk Assessment Tool” and our “Your Disease Risk” site at Washington University School of Medicine,” which offers estimates of 12 different cancers, including breast cancer. Unlike many tools available on the Web, these have been scientifically validated in published studies.

Web Resources

Washington University School of Medicine

Your Disease Risk

Twitter Feed - Your Disease Risk

8 Ways to Stay Healthy and Prevent Cancer (PDF)

Cancer Survivor's 8 Ways to Stay Healthy After Cancer (PDF)

Others

Harvard School of Public Health – Nutrition Source

National Cancer Institute

American Cancer Society

National Library of Medicine – PubMed

Environmental Contaminants: Recent Media Coverage Misleads on Preventability of Cancer

Tuesday, May 11, 2010 0 comments

Coverage of the President’s Cancer Panel report this week draws attention to environmental contaminants as a potential cause of cancer (report). While this is an area of much public interest and certainly an important part of comprehensive health policy, it is a strange focus for a report that is meant to influence the nation’s approach to cancer control and prevention. The excitement and fear this report is likely to stir up could direct efforts away from combating known lifestyle factors that have a much larger effect on cancer risk than environmental contaminants (see figure). Current evidence shows that pollutants cause just 1 - 4 percent of all cancer, while obesity and tobacco each cause 20 percent and 30 percent, respectively. Even when occupational exposures are added in, lifestyle factors trump environmental factors by at least a factor of six.

At a time when we know we’re in the midst of an obesity epidemic and we know that we’re not as physically active as we should be and we know that 20 percent of the population still smokes, why focus so much effort exploring a topic we also know has such a modest impact on risk? At its worst, it plays into the hands of tobacco companies and food manufacturers by deflecting discussions of harsher regulations onto other fields. If we acted with passion to remove causes of cancer as is proposed in the report for plastics, then clearly tobacco products would have been banned decades ago.

It’s only natural for humans to search for a magic bullet, that one thing that can easily fix it all – easily erase our cancer risk. Better studying and controlling environmental pollutants is an easy projection for this. But, the evidence clearly shows this would be no magic bullet. More than half of all cancer can be prevented with what we know today, and pollutants make up only a small part of this.

Below we summarize the known causes of cancer.

1. Tobacco

Established as the primary cause of cancer-related deaths and considered the single largest preventable cause of cancer in the world (1), the impact of tobacco on international health is hugely detrimental. Tobacco smoking causes bladder, cervical, esophageal, kidney, laryngeal, lung, oral, pancreatic, and stomach cancers and acute myeloid leukaemia (AML) (2). In the United States alone, smoking causes at least 30 per cent of cancer deaths annually; globally tobacco will kill more than five million people. Risk increases with daily consumption as well as duration of smoking. Second hand smoke poses significant risk as well, which makes tobacco the only legal consumer product that can harm everyone exposed to it.

Stopping smoking reduces future risk of cancer. For example, the reduction in risk of lung cancer is rapid with 50 percent risk reduction in less than 10 years (3). After more than 20 years, risk drops to near that of a never smoker.

2. Alcohol consumption

Alcohol is estimated to cause 4 per cent of all cancers in high income countries (4), with a higher burden in men than women, reflecting overall intake. Health risks increase with heavier drinking leading to oral cavity, pharynx, larynx, oesophagus, liver, breast and colorectal cancers (5). Risks increase further when heavy alcohol use is combined with smoking.

3. Physical activity

Globally, inactivity causes close to 2 million deaths each year (6). Lack of activity is linked to most major chronic diseases, including type II diabetes, osteoporosis, stroke, cardiovascular disease, and cancer. Based on a well-designed systematic review of published evidence, the World Cancer Research Fund reports there is “convincing” evidence that physical activity decreases risk for colon cancer, “probable” evidence of a decrease in postmenopausal breast cancer and endometrial cancer, and “suggestive” evidence of an impact on lung, pancreas, and premenopausal breast cancer (5). Growing evidence also points to physical activity substantially lower the risk of premenopausal breast cancer (7, 8) as well as other chronic diseases.

4. Weight control

Obesity is increasing at epidemic rates around the world (9). United States data from 2003-2004 show that 66 percent of adults are overweight or obese (BMI ≥25) and 32 percent of adults are obese (BMI ≥ 30). Since 1988, these rates have been steadily increasing (10).

Historical data from the past 25 years point to obesity as a cause of approximately 14 percent of cancer deaths in men and up to 20 percent of cancer deaths in women (11). These may be conservative estimates as the population has gained substantial weight over this time period, with the prevalence of overweight and obesity increasing from 15 percent in 1980 to 35 percent in 2005. The American Institute for Cancer Research (AICR) and World Cancer Research Fund (WCRF) reported there is convincing evidence for a relation between obesity and esophageal, pancreatic, colorectal, postmenopausal breast, endometrial and kidney cancers with probable evidence for cancer of the gallbladder. In addition, they found probable evidence that fat around the mid section (abdominal adiposity) in particular increases risk of pancreas, endometrial and postmenopausal breast cancer. Finally, emerging evidence suggests that obesity increases the risk of aggressive prostate cancer (12).

Overall, we estimate that overweight and obesity cause approximately 20 percent of all cancer. Previously, Doll and Peto (13) combined “overnutrition” (overweight) with diet and estimated that together they caused 35 percent of all cancer. We break out overweight and obesity from diet and provide updated estimates for the causes of cancer (figure).

The burden of obesity has increased so much that some now estimate that the total health burden of overweight and obesity may exceed that for cigarette smoking (14).

Public health recommendations call for adults to stay within the recommended BMI range (18.5-24.9) and avoid weight gain.

5. Diet and dietary supplementation

aflatoxin and liver cancer, and salt and stomach cancer, while non-starchy vegetables reduce risk of cancers of the mouth, oesophagus, and stomach (5). Because of benefits in preventing other major chronic diseases such as cardiovascular disease and diabetes, it is estimated that a global increase in fruit and vegetable consumption would save 2.7 million lives annually (6).

International recommendations prescribe a diet high in fruits and vegetables (at least 4-13 servings per day) with emphasis placed on nutrient-rich green leafy vegetables, orange vegetables, and legumes. Avoiding certain foods potentially decreases cancer risk, such as salt-preserved meats or other foods, red meat, and very hot food or drinks. The U.S. National Cancer Institute (NCI) recommends that only 20-35 percent of daily calories be from fat; comprised of primarily polyunsaturated or monounsaturated fats in fish, nuts, and vegetable oils, 10 per cent saturated fats, and as little trans fat as possible (15).

Substantial evidence supports a link between vitamin D and reduced incidence of colon cancer – the third most common cancer among both men and women in the United States. Studies show that people with higher circulating vitamin D levels can have as little as half the risk of developing colon cancer as those with lower vitamin D levels (16). This and other possible benefits were reviewed systematically by the International Agency for Research on Cancer (IARC) (16), and led to the recommendation that better understanding of possible adverse health effects of population supplementation, and the possible variation in benefits depending on the baseline serum 25-hydroxyvitamin D level, are necessary before recommending routine vitamin D supplementation for cancer prevention. Further research is needed to define the optimal dose or level of vitamin D, its efficacy in reducing cancer incidence, and the time course for change in risk of cancer after increasing levels.

6. Sun Exposure

The sun, as the primary source of ultraviolet radiation, poses a significant risk of skin cancer particularly in fair-skinned individuals. Internationally, nearly 60,000 deaths are attributed to over-exposure leading to malignant melanomas and skin cancer annually (17). Observing trends of increasing rates of skin cancer, the U.S. National Cancer Institute reports 60,000 new cases in 2007 in the United States alone (15). Prevention recommendations as simple as avoiding the sun in peak hours (approximately 10 am to 3 pm), covering skin whenever possible, protecting exposed skin with sunscreen, and avoiding tanning booths are effective in reducing skin cancer incidence if these lifestyle changes are adopted, particularly, at an early age.

7. Infections

Some 18 per cent of cancers worldwide can be linked to chronic infections due to agents such as Helicobacter pylori, human papillomaviruses (HPV), Hepatitis B, Hepatitis C, Epstein-Barr virus (EBV), human immunodeficiency virus (HIV), human herpes virus 8 (HHV-8), and Schistosoma haematobium (18), with the proportion of all cancer due to infections being much higher in developing countries (26 per cent, compared to 7.7 per cent in developed countries). The current burden of cancer in the developing world is dominated by infection, once smoking is accounted for. (See related post) .

8. Environmental and occupational exposures

Environmental exposures account for 1-4 percent of cancers. Occupational exposures such as asbestos, arsenic in drinking water, food contaminants such as aflatoxins and pesticides, and radiation exposure are classified as environmental carcinogens, but in countries with established market economies, exposure is now largely limited by regulation to reduce harm. International agencies have responded by identifying carcinogens (e.g., IARC classification of carcinogenic compounds) and regulating use, exposure, and protection for employees in the case of occupational hazards.

As better regulations of contaminants have been put into place in the most developed countries, production has been exported, in some cases, to countries with more lenient requirements for environmental exposure and contaminants thereby not eliminating, but shifting, the cancer risk from an international scope. Despite regulatory changes in many countries, exposure to asbestos, for example, continues through occupations such as construction, ship work, and asbestos mining. Given the long lag between exposure and lung and pleural cancers, mortality from asbestos-related disease is estimated to remain at 90,000 per year (19).

Successful enforcement of approaches to reduce exposure to known carcinogens in both the work place and the home is necessary to achieve successful cancer prevention.

9. Medications

Medication use is widespread in high income countries and limited in low and middle income countries. Strong evidence supports several medications as either causing cancer – for example, postmenopausal hormone therapy with estrogen plus progestin (20) - or reducing cancer - for example, oral contraceptives and ovarian cancer (21), and aspirin and colon cancer (22).

For combination estrogen plus progestin, the IARC has now classified this combination therapy as carcinogenic in humans (23) and estimates indicate that the reduction in use of hormones after the widespread publicity of the results of the Women’s Health Initiative (stopped early due to excess breast cancer) accounts for approximately a 10 percent decline in incidence among women 40 - 70 years of age (20). Thus for this combination therapy, evidence shows that risk rises with duration of use and that acting as a late promoter, removal of the drug leads to a rapid decline in incidence (20), though among women with longer durations of use risk may not return to that of women who have never used combination therapy (24). Other less widespread drugs may also contribute to cancer risk (such, DES), but the population impact will be substantially smaller because of their relatively low use in the population.

For some medications that reduce risk, the benefits have been limited to date to those who have had specific indications for use of the medication. Broader population strategies may be developed for more widespread protection, such as could be achieved if all women took oral contraceptives as a chemopreventive for a minimum of 5-years

Related CNiC posts:

On Prevention

On Policy

Literature cited:

1. Peto, R., et al., Mortality from smoking worldwide. Br Med Bull, 1996. 52(1): p. 12-21.

2. U.S. Department of Health and Human Services, The health consequences of smoking: a report of the Surgeon General. 2004, Centers for Disease Control and Prevention: Washington, DC.

3. Kenfield, S.A., et al., Smoking and smoking cessation in relation to mortality in women. Jama, 2008. 299(17): p. 2037-47.

4. Danaei, G., et al., Causes of cancer in the world: comparative risk assessment of nine behavioural and environmental risk factors. Lancet, 2005. 366(9499): p. 1784-93.

5. World Cancer Research Fund, Food, Nutrition, Physical Activity, and the Prevention of Cancer: a Global Perspective. 2007, Washington, DC: AICR.

6. Ezzati, M., et al., Selected major risk factors and global and regional burden of disease. Lancet, 2002. 360(9343): p. 1347-60.

7. Bernstein, L., et al., Physical exercise and reduced risk of breast cancer in young women. J Natl Cancer Inst, 1994. 86(18): p. 1403-8.

8. Maruti, S.S., et al., A prospective study of age-specific physical activity and premenopausal breast cancer. J Natl Cancer Inst, 2008. 100(10): p. 728-37.

9. International Agency for Research on Cancer, Weight Control and Physical Activity. IARC Handbook on Cancer Prevention. Vol. 6. 2002, Lyon: International Agency for Research on Cancer. 315.

10. Ogden, C.L., et al., Prevalence of overweight and obesity in the United States, 1999-2004. JAMA, 2006. 295(13): p. 1549-55.

11. Calle, E.E., et al., Overweight, obesity, and mortality from cancer in a prospectively studied cohort of U.S. adults. N Engl J Med, 2003. 348(17): p. 1625-38.

12. Freedland, S.J. and E.A. Platz, Obesity and prostate cancer: making sense out of apparently conflicting data. Epidemiol Rev, 2007. 29: p. 88-97.

13. Doll, R. and R. Peto, The Causes of Cancer: Quantitative Estimates of Avoidable Risks of Cancer in the United States Today. 1981, New York: Oxford University Press.

14. Stewart, S.T., D.M. Cutler, and A.B. Rosen, Forecasting the effects of obesity and smoking on U.S. life expectancy. N Engl J Med, 2009. 361(23): p. 2252-60.

15. National Cancer Institute, Cancer Trends Progress Report – 2007 Update. 2007, NIH, DHHS: Bethesda, MD.

16. International Agency for Research on Cancer, Vitamin D and Cancer. 2008, International Agency for Research on Cancer: Lyon.

17. World Health Organization, The World Health Organization's Fight Against Cancer: Strategies that prevent, cure, and care. 2007, World Health Organization: Geneva.

18. Parkin, D.M., The global health burden of infection-associated cancers in the year 2002. Int J Cancer, 2006. 118(12): p. 3030-44.

19. World Health Organization, Elimination of Asbestos-related Disease, in Public Health and the Environment. 2006, World Health Organization: Geneva.

20. Colditz, G.A., Decline in breast cancer incidence due to removal of promoter: combination estrogen plus progestin. Breast Cancer Res, 2007. 9(4): p. 108.

21. Collaborative Group on Epidemiological Studies of Ovarian, C., et al., Ovarian cancer and oral contraceptives: collaborative reanalysis of data from 45 epidemiological studies including 23,257 women with ovarian cancer and 87,303 controls. Lancet, 2008. 371(9609): p. 303-14.

22. Chan, A.T., et al., Long-term use of aspirin and nonsteroidal anti-inflammatory drugs and risk of colorectal cancer. JAMA, 2005. 294(8): p. 914-23.

23. International Agency for Research on Cancer, Combined estrogen-progestogen contraceptives and combined estrogen-progestogen menopausal therapy. IARC Monogr Eval Carcinog Risks Hum, 2007. 91: p. 1-528.

24. Colditz, G.A. and B. Rosner, Cumulative risk of breast cancer to age 70 years according to risk factor status: data from the Nurses' Health Study. Am J Epidemiol, 2000. 152(10): p. 950-64.

Oral Contraceptives – 50 Years of Progress in Women’s Health

Sunday, May 9, 2010 0 comments

Numerous recent media reports highlight the historic progress in women's health with development and marketing of oral contraceptives. As Collins reported in the New York Times (column), we celebrate the 50th anniversary of the birth control pill. She notes the need for information on contraception and the challenges women had historically obtaining accurate data. Over the past 50 years much research has focused on contraceptives methods their risks and benefits. As we have noted previously, benefits of oral contraceptives can be substantial. Media attention, however, often focuses on potential adverse effects such as venous thrombosis and pulmonary embolism, the benefits of prevention are not identified at the individual level and hence often ignored.

Contraception avoids not only unintended pregnancies, but also millions of abortions and many pregnancy related deaths. These global benefits are detailed in a report from the Alan Guttmacher Institute in New York. (report). US data indicate that among women 15 to 49 years of age 72.8% are using a method of contraception, 21.2 % repot female sterilization, 9.7% male partner sterilization, and 18% are using contraceptive pills (report).

A rigorous systematic review of contraceptive methods and effectiveness shows that failure varies by approach and by the level of adherence to “perfect use” (review). Combining data from epidemiologic studies show significant reduction in risk of ovarian cancer, endometrial cancer and colon cancer as well as dysfunctional uterine bleeding, and ovarian cysts.

Risk of ovarian cancer is reduced by 20 percent for each 5 years of use. After 15 years of use a woman’s risk is half that of what it would be if she had never user the contraceptive pill. The benefit of reduced ovarian cancer persists after stopping use.

The combined evidence shows without doubt that the pill is safe and has major benefits including a reduction in the level of cancer among users. Like many other prevention benefits, particularly those for cancer, the time course is long and the beneficiaries are largely unknown. This time to benefit clearly contrasts with the immediate benefit related to the indication for using the pill - avoidance of conception – a benefit that is observed each month.

Health care reform and prevention of cancer

Wednesday, April 7, 2010 0 comments

In Sunday's New York Times (story), Robert Pear wrote about the many disease prevention initiatives contained in the new health care law recently passed by congress and signed by the president. It's important to stop and consider the full implications of this.

Importantly, Medicaid will now cover drugs and counseling to help pregnant women stop smoking. This will have substantial public health benefit. Worksites allowing a reasonable break time for nursing mothers to either nurse of pump milk will not only be of benefit for the infant being breastfed but also for the mother, as longer durations of breastfeeding significantly reduce risk of ovarian cancer and breast cancer. This long term benefit to new mothers is often overlooked in policy debates.

Access to screening is also positioned as a benefit of the new law. Yet, we should not forget that access alone does not remove disparities in the cancer burden. Strong evidence from Medicare shows that with access to colon cancer screening in place, levels of screening have risen over time. Importantly this increase has been observed across race and education levels. However, significantly lower rates of screening for colorectal cancer are observed among less educated older adults. As of 2005 among Medicare beneficiaries, rates of colon cancer screening were 20 percent lower among those with a less-than-high school education compared to those with a greater-than-high school education (study link) (1). Similar disparities were observed by income level.

The clear message is that we must continue to focus prevention messages and strategies on ways to reach such groups so they too can gain the benefits of cancer prevention through colorectal screening. We cannot ignore the powerful data that come from Medicare through the past decade. Prevention efforts must focus on strategies that bring participation in prevention to a common level across society. Only then will we achieve the benefits of wellness for all regardless of age, education and income.

For more on cancer prevention, see: http://knol.google.com/k/cancer-prevention#

Literature cited

Doubeni, C.A., et al., Socioeconomic and racial patterns of colorectal cancer screening among Medicare enrollees in 2000 to 2005. Cancer Epidemiol Biomarkers Prev, 2009. 18(8): p. 2170-5.

Oral contraceptives reduce cancer deaths

Tuesday, March 30, 2010 0 comments

A recent study in the British Medical Journal adds further evidence that use of oral contraceptives reduces cancer mortality (full study). In the long term study of over 46,000 women who were followed for up to 39 years, Hannaford and colleagues reported that women who used oral contraceptives (OCs) had lower mortality from cancers of the ovary, uterine body and colon (Hannaford, Iversen et al. 2010). OC use was not related to breast cancer mortality.

Approximately half of the women who had used OCs had used them for more than 4 years, and the risk of cancer death decreased the longer women had used OCs. These data extend previous work from the Nurses’ Health Study, which showed no overall adverse effect from use of OCs (Colditz and for the NHS research group 1994).

Oral contraceptives are one of the most widely used medications. Use of oral contraceptives (OCs) for 5 years halves a woman’s risk of developing ovarian cancer (see figure) and substantially reduces the risk of endometrial cancer (Collaborative Group on Epidemiological Studies of Ovarian, Beral et al. 2008).

Data source: Beral et al, 2008 (click figure to enlarge)

The protection is long lasting and in high income countries rates of use approach 80 per cent. Adverse effects are largely limited to an increased risk of breast cancer and stroke while women are currently using OCs, a risk which seems to disappear within about ten years of stopping. These side-effects are strongly age-dependent - being more common the older a woman is. Thus use of OCs during late teens and early 20s could be expanded for greater reduction in ovarian and endometrial cancers and overall net public health benefit (Kawachi, Colditz et al. 1994).

Strong scientific evidence supports several other medications as either causing cancer (e.g. postmenopausal hormone therapy with estrogen plus progestin) (Colditz 2007), or reducing cancer (e.g aspirin and colon cancer) (Chan, Giovannucci et al. 2005).

Postmenopausal hormones
For combination oestrogen plus progestin, the International Agency for Research on Cancer (IARC) has now classified this combination hormone therapy as carcinogenic in humans (2007), and estimates indicate that the reduction in use of hormones after the widespread publicity of the results of the Women’s Health Initiative (stopped early due to excess breast cancer) accounts for approximately a 10 per cent decline in breast cancer incidence among women 40 to 70 years of age (Colditz 2007). Thus for this combination therapy evidence shows that risk rises with duration of use and that acting as a late promoter, removal of the drug leads to a rapid decline in incidence (Colditz 2007), though among women with longer durations of use risk may not return to that of women who have never used combination therapy (Colditz and Rosner 2000).

Other less widespread drugs may also contribute to cancer risk (e.g., DES), but the population impact will be substantially smaller than the examples based on much more widespread use described above.

For some medications that reduce cancer risk, the benefits have been limited to date to those who have had the specific indications to use the medication. Broader population strategies may be developed for more widespread protection, such as could be achieved if all women took oral contraceptives as a chemopreventive for a minimum of 5-years.

Aspirin
Aspirin has been extensively studied in observational studies that address duration of use, dose, and magnitude of risk reduction. This evidence is consistent with evidence from randomized primary prevention trials showing that the use of 300 mg or more of aspirin a day for 5 years or more is effective in preventing colon cancer; reducing risk by approximately 25 per cent (Flossmann and Rothwell 2007). A latency of about 10 years is observed between onset of use of aspirin and the reduction in cancer. Like all chemoprevention strategies, risks and benefits must be balanced (Glasziou and Irwig 1995). To date, the risk-benefit considerations of cardiovascular disease, bleeding complications, stomach pain and heart burn caused by aspirin have precluded recommendations for aspirin use as a widespread prevention strategy (Gralow, Ozols et al. 2008).

Selective estrogen receptor modulators (SERMs)
Selective estrogen receptor modulators (SERMs), such as tamoxifen and raloxifene, have been shown in randomized controlled prevention trials to reduce incidence of pre-invasive and invasive breast cancer (Fisher, Costantino et al. 1998; Martino, Cauley et al. 2004). While tamoxifen increases risk of uterine cancer, this is not so for raloxifene and the risk profile for raloxifene looks considerably safer (Chen, Rosner et al. 2007).

Based on these risks and benefits of therapy, we have estimated the potential for risk reduction among women over age 50 who are postmenopausal. Our estimates indicate that if the trade-off of excess adverse events versus cases of breast cancer prevented must be less than 1, then approximately 30 per cent of the 27 million women between ages 50 and 69 in the United States have benefits exceeding risks, and would achieve a 50 percent reduction in the burden of breast cancer by taking a SERM. This is a population benefit of 42,900 fewer cases of invasive breast cancer among the more than 7 million women with sufficiently high risk to justify chemoprevention (Chen, Rosner et al. 2007).

The reduction in breast cancer risk observed in the chemoprevention randomized trials is very rapid; within 2 years of beginning SERM therapy, incidence curves have clearly separated. This is consistent with the pharmacologic action of these agents inhibiting estrogen receptors. Importantly these agents show protection against estrogen receptor (ER) positive breast cancers (risk reduction up to 76 per cent) and no protection against receptor negative cancers (Martino, Cauley et al. 2004).

While statistical models to predict and classify risk of breast cancer have been developed and validated, to date, prediction of receptor positive tumors is no more accurate than prediction of risk overall (Colditz, Rosner et al. 2004). Refining risk stratification and developing tools to aid women in considering trade-offs of risks and benefits of chemoprevention therapy are necessary next steps to informed choices for prevention for women at elevated risk of breast cancer.

Conclusions
While all drugs have risks and benefits, some of the agents described here have the potential to substantially reduce risk of cancer. Balancing risks and benefits remains an important decisions that should be reviewed with a heath care provider.

Literature cited

Chan, A. T., E. L. Giovannucci, et al. (2005). "Long-term use of aspirin and nonsteroidal anti-inflammatory drugs and risk of colorectal cancer." JAMA 294(8): 914-923.

Chen, W. Y., B. Rosner, et al. (2007). "Moving forward with breast cancer prevention." Cancer 109(12): 2387-2391.

Colditz, G. and for the NHS research group (1994). "Oral contraceptive use and mortality during twelve years of follow-up." Ann Intern med 120: 821-826.

Colditz, G. A. (2007). "Decline in breast cancer incidence due to removal of promoter: combination estrogen plus progestin." Breast Cancer Res 9(4): 108.

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